1. Field of the Invention
The present invention relates to undersea relocation systems and more particularly relates to a system for relocating an underwater object by means of a retrievable marker buoy which is released to the surface responsive to a received acoustic signal, carrying with it the free end of a contained canister line and preferably an acoustic signal receptive release transponder.
2. General Background
It is frequently desirable to relocate an object underwater such as, for example, an abandoned oil well, a subsea wellhead or "Christmas tree" as well as pipeline valves, pipeline crossings, completions and the like. In addition, it is desirable to be able to repeatedly relocate anchor pennant lines for retrieval as these lines are used with floating rigs, dredges, etc.
Often times objects to be relocated are in water which is of low visibility and which can be very deep. In addition, the relocation may need to be performed during a time in which the water surface is rough complicating relocation efforts. Many systems have been patented attempting to solve the problem of undersea relocation. Some such devices have used an explosive charge to disengage a buoyed system from its anchor. Other devices have used an explosive charge to inflate a bag-type buoyancy module to provide the needed uplifting force to cause a system to ascend. Such explosive devices are both unreliable and can cause environmental damage in the form of, for example, fish kills. Other devices have used a search or tag line that is wound around that portion of the buoyant component which ascends to the surface. This method of paying out the search line can be unreliable as the line must unwind from the buoyancy component which is in motion and the line can often fowl and/or get tangled as it is paid out from the erratically wiggling buoy.
As an example of such previously patented devices, note for example, U.S. Pat. No. 3,722,014 issued to Hill, et al, entitled "Retrievable Buoy." That patent provides a retrievable submersible buoy which is anchored at an underwater location and includes an explosive charge release mechanism which releases the buoy from its anchor in response to a remotely actuated signal.
U.S. Pat. No. 3,889,307 issued to Georges Houot is entitled "Remote-Controlled Underwater Buoy." The '307 patent provides a remote-controlled, immersed buoy which allegedly makes it possible to connect an object placed on the ocean floor to the surface by means of a wire rope and includes a body member kept in the immersed position by a latching assembly which is capable of being freed by a beacon upon reception of an acoustic signal. A wire rope attached to an anchoring element winds on a drum as the buoy is raised. A removable electric motor is used to wind the wire rope on its drum to bring the buoy to the immersed position.
U.S. Pat. No. 3,487,486 is of a type which is normally immersed and which can be raised to the surface in response to a remote control signal. This type of buoy comprises abody element connected by a cable to an anchoring element lying on the sea bottom and a thrust device bringing the body member to the surface under the action of a release mechanism remotely controlled from the surface. When the buoy floats, a wire rope is used for linking the anchoring element with the surface.
In oceanography, it is known to set up a current recorder on or near the ocean bottom for the monitoring of various parameters such as water temperatures, salinity, p.h., flow rates, and to collect this recorded data at the end of a desired time interval. In order to do this, it is necessary to retrieve the recorder after the desired time period and to disassemble the recorder in order to get the information contained within. One device which has been used in the past for the undersea placement of such recorders is a digital acoustic command system which is marketed under the trademark "SEA LINK." Such a system is based on an acoustic code from a ship board or surface vessel that is transmitted through the water to an underwater unit. If the code or codes are accepted by the unit a command function is actuated. This command function may be a mechanical release of the underwater unit, a command to shut down or turn on the underwater unit or an external control signal to actuate a valve, for example. Such systems as the "SEA LINK" consist of a shipboard unit with a transducer and one or more underwater units. The standard underwater units incorporate a transponder with a release mechanism and can have additional commands available. Underwater units can contain various command decoders for external command functions. Such underwater units known as release/transponders can be used at depths of up to, for example, twenty thousand (20,000) feet.
U.S. Pat. No. 3,775,736 entitled "Acoustical Underwater Control Apparatus" provides an apparatus for controlling the operation of underwater equipment from the surface by wireless signals and monitoring the status of underwater equipment. A power source is provided for continuously supplying power to the underwater system. A minimal number of hardline connections are provided between the surface and underwater units.
An "Oceanographic Apparatus" is the subject of U.S. Pat. No. 3,287,753. That patent relates to oceanographic devices and more particularly to an underwater buoy having a floatable portion which may released in response to sonic signals from a remote transmitter.
A "System for Activating a Remote Underwater Device" is the subject of U.S. Pat. No. 3,742,440. A frequency coded acoustic wave generator is used having at least one notch frequency in the transmission spectrum. The generator is adapted to transmit simultaneous assertion and negation frequencies. An acoustic responsive receiver is located at the remote underwater device. The receiver includes a code validation logic arrangement responsive to each received acoustic wave verifying the simultaneous presence and absence of the assertion and negation frequencies. A utilization circuit also in the receiver is responsive only to a verification signal from the validation logic.
An underwater "Hydraulic Latch" is the subject of U.S. Pat. No. 3,553,795 issued to D. E. McDougal.
An "Underwater Transponder Calibration Arrangement" is the subject of U.S. Pat. No. 4,097,837.
These devices as aforementioned frequently use explosive charges to disengage the system. Some are very complex and can be unreliable. Some are not easily operated and are prone to malfunction.
While some attempt to provide a float which carries a line to the surface, many are not self-contained and rugged enough to be left for long periods of time beside a desired object to be located later and then still operate after such time without extraneous complex connections being necessarily made first by a diver.
3. General Discussion of the Present Invention
The present invention provides a subsea acoustic relocation apparatus having a portion for anchoring a line canister at the seabed which canister has an opening through which a contained canister line can pay out. The canister line is placed within the line canister and is anchored at one end to the canister, the other end being a free end which dispenses from the canister during operation. An acoustic transponder release detachably affixes to the frame at a provided removable connection which can be broken by an acoustic signal. The acoustic transponder having attached thereto the free end of the canister line with the temporary connection affixing the free end to the seabed at a provided anchor. A buoyant float is provided for carrying the free end of the canister line to the water surface responsive to a breaking of the removable connection. In one embodiment a weighted frame supports a canister and the transponder/release. In that embodiment, a cradle on the frame supports the buoy on the frame prior to release of the removable connection, thus providing a structurally integral, self-contained apparatus that can be easily transported.
The buoy is of a sufficient buoyancy value to lift the free end of the canister line (and preferably the attached acoustic transponder), but its buoyancy value is insufficient to overcome the provided seabed anchor. A flexible sling can be provided connecting the buoy with the frame allowing the buoy to tether a distance above the canister once the buoy is submerged. The line canister and the acoustic transponder release means can be placed side-by-side within the casing bore with their longitudinal axes generally parallel.
With the frame embodiment, the cradle can comprise a plurality of struts extending upwardly from the frame and supporting at their uppermost ends, the buoy. The buoy can be a spherical buoy with each of the struts supporting the spherical buoy at its lower half so as not to interfere with upward movement of the buoy when desired.
The apparatus can provide a pressure sensitive strob light carried by the buoy for emitting a lighted signal responsive to movement of the buoy to the water surface.
The buoy and the acoustic transponder release assembly can rise together to the water surface when the removable connection is broken. In such an embodiment, the buoy would have sufficient buoyancy to lift both the free end of the canister line and the acoustic transponder release assembly.
In the method of the present invention, the assembly is anchored at or near a desired object to be relocated at a future designated relocation time. Provided is a line canister having a canister line therein with one end of the canister line anchored to the seabed area and the other end being a free end which is attached to a buoyed structure which can lift the canister line free end but not overcome the anchor. The buoyed structure is secured at the seabed with a removable connection that can be broken with an acoustic signal. An acoustic signal is emitted by a surface vessel, for example, at the designated relocation time causing the buoy and the free end of the canister line to rise to the water surface area.